Subjects were eye-tracked while watching videos of real driving scenes with or without a HUD. In Condition 1 subjects reported what elements in the video attracted their attention in real time (Charlton, 2006). This was followed by a sign recognition test. In Condition 2 subjects engaged in casual conversation while watching another driving video. Warning signs were more conspicuous in low and high clutter driving environments with a HUD. The HUD did not lead to increased fixation duration or frequency for warning signs except when two driving relevant targets were in view (a sign and oncoming car). While the HUD highlighted a warning sign there were fewer fixations on the car compared to the non-HUD situation. Condition 1 showed augmented reality (AR) HUDs can make warning signs more salient to drivers. When there were multiple driving relevant stimuli in high clutter environments, AR HUDs may induce attentional tunneling.